the IP address assignment thing, where did they get that from?
They are talking about generic ISPs and thats how it would usually occur.
But what you must bear in mind that BTw serves not just BT, but also many other ISPs... and therefore can and does use L2TP to hide things that sole providers wouldnt bother with.
Authentication occurs at the RAS using BT RADIUS servers. So in geographic terms IPs are indeed allocated at the RAS. However, BTw RADIUS 'talks' to the ISP RADIUS server to get an IP.
Sometimes if stage 2 ISP authentication fails, then you can find yourself issued with a BT IP address, but its useless in that you cant go anywhere outside of BTw's network.
There's some diagrams on the WBC/MBMC pages
that show the BTw RADIUS and ISP RADIUS links during the authentication process.
Is that true? Certainly isn't true for me!
The 20CN page
also has a bit more info on Authentication and also a link
that shows the full process where the RADiUS allocates the IP.
You yourself phyically dont see this because AAISP uses shared WBMC... and BTw uses L2TP to hide much of whats going on in the background. For shared WBMC you dont see anything before the ISP gateway.
If the ISP (such as BTr or Plusnet) uses dedicated WBMC, then the EU can usually still see the RAS IP as theres no L2TP to hide the RAS hops.
BTW, the new MSE bRAS IP allocation is quite interesting for WBMC dedicated ISPs... as the ISP allocates a pool of their IPs that each MSE bRAS can use, rather than one great big dynamic pool. Remember MSE bRAS can be very close location-wise now for a lot of people. What I dont particularly like about this is if say that pool only has a few hundred IPs then it can very closely identify your location if the person who had the IP before you was careless about geolocation tags. Its also why some Plusnet users also moan that they can't pick up a different IP other than say the last couple of digits and may even be constantly given the same IP.
Plusnet Static IPs are slightly different and not dished out from the local pool. It looks like they are using their steering server (again seen in the WBMC diagram) to direct to certain gateways and still use L2TP.